1. Field of the Invention
The present invention relates to a reel on which a recording tape, such as a magnetic tape or the like, is wound, and to a recording tape cartridge which rotatably accommodates the reel within a case.
2. Description of the Related Art
Recording tapes such as magnetic tapes and the like are used as external recording media for computers and the like. Little space is required to accommodate such a recording tape at the time of storage thereof, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used in which a single reel, on which the recording tape is wound, is rotatably accommodated within a case.
A reel which is made of resin and which structures such a recording tape cartridge will be described by using FIG. 10. The axially central portion of a reel 200 shown in FIG. 10 is structured by a reel hub 202. The reel hub 202 is formed in the shape of a cylindrical tube having a bottom, and a magnetic tape is wound around the outer peripheral surface thereof. The reel hub 202 has an engaging gear 206 which stands at the inner surface of a floor plate portion 204 of the reel hub 202, and a reel gear 208 which stands at the outer surface of the floor plate portion 204.
The engaging gear 206 is formed by a large number of teeth, whose addenda are directed upward, the teeth being disposed along a circumference which is coaxial with the reel hub 202, and is provided on a pedestal portion 210 which stands erect at the floor plate portion 204. When the magnetic tape is not being used, the engaging gear 206 meshes with a braking gear which is formed at the bottom surface of a braking member, so as to impede rotation of the reel 200. The respective teeth of the engaging gear 206 are formed in tapered shapes which guide the braking gear in. The engaging gear 206 centers the braking member by meshing with the braking gear which is adjacent thereto along the axial direction of the reel hub.
Because the respective teeth of the engaging gear 206 are formed in tapered shapes, there is the concern that the reel 200 will rotate merely due to the braking member moving slightly from the locked state of the reel 200 in the direction in which locking is released.
On the other hand, the reel gear 208 is formed by a large number of teeth, whose addenda are directed downward, the teeth being disposed along the outer peripheral portion of the floor plate portion 204. The radial direction inner side end portions of the respective teeth are connected by a rib 212. A reel plate 214, which is formed of a magnetic material, is attached to the inner side of the rib 212 at the outer surface of the floor plate portion 204. The reel plate 214 is attracted by a magnet provided at the rotating shaft of a drive device. When the magnetic tape is used, a driving gear of the aforementioned rotating shaft meshes reel gear 208 in a state in which the reel plate is attracted to and held by the magnet. Due to the rotating shaft rotating in this state, the reel 200 is driven to rotate.
However, at the reel 200, as shown in FIG. 11, the engaging gear 206 is formed on the pedestal portion 210, and the rib 212 projects from the reverse side of this pedestal portion 210. Therefore, a thickness t4 of the floor plate portion 204 of the reel hub from the top surface of the pedestal portion 210 (the engaging gear 206) to the bottom surface of the rib 212 is large. Moreover, at the radial direction inner side of the portion where the thickness is t4, a portion having a thickness t5 from the pedestal portion 210 to the bottom surface of the floor plate portion 204, and a portion having a thickness t6 which is the thickness of the floor plate portion 204 itself, are formed continuously in that order. Namely, this is a structure in which the thickness changes in steps. The flowability of the resin at the time of molding the reel 200 is therefore poor.
Moreover, at the reel 200, the surfaces of the reel gear 208 which mesh with the driving gear are inclined surfaces which are inclined with respect to the axial direction. The positioning of the reel 200 in the axial direction with respect to the rotating shaft is carried out by the reel gear 208 and the driving gear meshing together such that no backlash arises. Namely, the axial direction reference surface at the time when the reel 200 is driven to rotate is an imaginary surface which is the meshing pitch surface of the reel gear 208 with the driving gear. In this way, because the dimensions of the respective portions of the reel 200 are determined on the basis of an imaginary reference surface, evaluation of the dimensions of the respective portions, and designing, have been complicated.
Thus, as disclosed in U.S. Pat. No. 6,273,354 for example, the following structure has been conceived of in which: three convex portions for reference project at uniform intervals in the peripheral direction from the outer surface of the floor plate portion of the reel hub, at the radial direction outer side of the reel gear; end surfaces of the respective convex portions for reference, which are surfaces orthogonal to the axis of the reel, are used as reference surfaces; and positioning of the reel in the axial direction is carried out by these reference surfaces being made to abut positioning surfaces of the rotating shaft.
However, even in a structure in which such reference surfaces are provided independently of the reel gear, there is room for improvement.